1. Field of the Invention
The invention pertains to the art of impeller and shaft assemblies for centrifugal gas compressors such as are used in relatively large air-conditioning machinery and in which the impellers rotate at speeds of 10,000 to 30,000 revolutions per minute and up.
2. Description of the Prior Art
It is relatively important that centrifugal gas compressor impellers and shaft mounting arrangements for such machines be such that adequately high torque capacity be provided while also permitting removal and reinstallation of the impeller to the shaft without undue difficulty.
In the known commercial art, one arrangement which functions satisfactorily on compressors of a given size is disclosed in U.S. Pat. No. 3,601,501 and discloses conically shaped washers and impeller surfaces which mate and provide a friction fit with the parts held tightly together by a cap screw.
Another current arrangement in generally satisfactory use for certain centrifugal gas compressors has spiral threads machined on both the front end of the driving shaft and the mating surface at the rear of the impeller wheel, the spiral threads being required to be carefully mated when the wheel is installed. However, this arrangement has several disadvantages. For example, the machining of the threads is relatively difficult and expensive. To check that the threads are correctly machined, a given dimension ball is rolled in the grooves for their length to determine correct groove depth. In installation, this spiral threaded arrangement is neither self-centering nor self-aligning to the degree desired to be attained in connection with my invention.
Also in the known prior art, both U.S. Pat. No. 1,403,309 and No. 2,119,334 disclose shaft and gear or pulley arrangements in which spirally directed grooves or protrusions are provided in one or the other of the parts so that the material of one of the parts will be displaced in the pattern of the spiral on the other part to promote a tight connection.
None of these arrangements is considered to have all of the advantages of the arrangement according to my invention, which provides a high torque capacity, is relatively easy to machine and install, is self-centering and self-aligning in installation, and permits closer tolerances to be held so that vibration and seal damage of high speed impellers is reduced.